Chemical surface modification of porous silicon layers with porosity P = 75% was performed by placing the layers into a tetraethoxysilane (TEOS)/ethanol/water solution. The duration of this treatment t(T) was varied from 3 h to 232 h. Infrared (IR) reflectance spectra show a decrease of Si-H vibrations and a strong increase of Si-O vibrations with increasing t(T). Additionally, the mass variation of these layers was determined. Photoluminescence (PL) spectra of the modified samples show a continuous increase in the integral PL intensity (up to sixfold) and a slight red-shift (up to 0.07 eV) with increasing t(T). Time-resolved PL measurements were performed in order to study the effect of tetraethoxysilane (TEOS) treatment on non-radiative luminescence mechanisms within the silicon crystallites. TEOS treatment was also applied on highly porous layers with P = 80, 85 and 88% resulting in non-destructive subcritical drying and bright luminescence of these layers.